Design and synthesis of nickel-containing covalent organic frameworks for visible light induced directed ortho-trifluoromethylation of aromatic amides

A nickel based covalent organic framework (Ni(II)@TFPA-COF) was designed and synthesized by bonding the double bonds of olefins and imines formed through orthogonal Schiff base reaction and Knoevenagel condensation using 4-aminobenzyl cyanide and tris-(4-formylphenyl) amine as starting materials, and its structure and optical properties were characterized. Ni(II)@TFPA-COF was used as a recyclable catalyst to develop a visible-light-induced reaction strategy for the directed ortho-trifluoromethylation of aromatic amide, and a series of ortho-trifluoromethylated aromatic amides were synthesized with good yields under mild and green conditions. Ni(II)@TFPA-COF exhibited good dual-functionality in photocatalysis and transition metal catalysis in the reaction. Based on the control experiments and literatures, a possible reaction mechanism for visible-light-induced directed C–H activation was proposed. This provides a novel, green, sustainable and efficient solution for the ortho-trifluoromethylation reaction of aromatic amides.